This application claims the priority of Japanese Patent applications No.10-323318, No. 10-323319 and No. 10-323320 filed on Nov. 13, 1998, and No. 11-194412 filed on Jul. 8, 1999, which are incorporated herein by reference.
1. Field of the invention
This invention relates in general to a skin cleanser, and more particularly to a weak acid skin cleanser which has creamy and rich foaming, rapid rinsing, and a moist skin sensation after cleaning when used for skin cleaning for the purpose of cleaning off skin stains and sebum.
2. The Prior Art
Conventionally, soap, which is an alkali salt of a fatty acid, has been used as the base cleanser of a cleanser for the purpose of washing skin.
It is well known that soap has a superior cleaning effect and is superior in terms of giving agreeable sensations during skin cleaning such as creamy and rich foaming, rapid rinsing, and a refreshing sensation, and therefore is used as cleansing foam, bath soap, and face washing soap in many skin cleaning applications.
However, on the other hand, the refreshing sensation of soap is so strong that a moist and agreeable sensation after cleaning is hard to obtain. Despite blending in various oil components and/or synthetic surfactants in a cleanser or adjustments in the recipe by changing the soap content and such, a moist skin sensation after cleaning cannot be obtained in practical use.
Also, a feature demanded by consumers for a skin cleanser is to have weak acidity which is close to skin pH. However, recipes whose main ingredient is soap, which is intrinsically highly alkaline, cannot respond to such a demand.
For the purpose of obtaining a weak acid skin cleanser which has a superior cleaning effect, gives agreeable sensations during skin washing such as creamy and rich foaming, rapid rinsing, and a refreshing sensation, as well as a superior moist skin sensation after cleaning, and thus responds to consumers"" demand, base cleansers other than soap including alkali salts of acylglutamic acid, alkali salts of acylsarcosinic acid, alkali salts of alkylsulfosuccinic acid, and alkali salts of alkylphosphoric acid have been used.
However, they have problems with at least one item in the group of items that includes the cleaning effect, creamy and rich foaming, rapid rinsing, refreshing sensation during use, moist skin sensation after cleaning, and shelf stability of the base agent (separation, offensive odor, discoloration, etc.). It has been very difficult to obtain a weak acid cleanser which is satisfactory in all these aspects.
In view of the aforementioned problem, the inventors conducted earnest research to develop a weak acid cleanser which has a satisfactory effect in terms of all these items, which include the cleaning effect, creamy and rich foaming, rapid rinsing, refreshing sensation during use, moist skin sensation after cleaning, and shelf stability of the base agent (separation, offensive odor, discoloration, etc.). As a result, we discovered that a weak acid skin cleanser which contains alkali salt of N-acylamino acid and maltitolhydroxy aliphatic ether, or a hydroxy ether carboxylic acid-based anionic surfactant, or polyethylene powder can beautifully solve the aforementioned problem, thus completing the present invention.
The object of the present invention is to develop a new weak acid skin cleanser which is superior in terms of the cleaning effect, creamy and rich foaming, rapid rinsing, refreshing sensation during use, moist skin sensation after cleaning, and shelf stability of the base agent (separation, offensive odor, discoloration, etc.) and thus responds to consumers"" demand.
However, when the aforementioned cleanser base agent was used to prepare a skin cleanser in a paste form, there was a fatal problem in that the hardness increased over time at room temperature or lower temperatures and therefore the skin cleanser became hard to squeeze out of a tube.
In view of the aforementioned problem, the inventors conducted earnest research to develop a cleanser which does not have a problem in that the hardness increases over time at room temperature or lower temperatures and therefore the skin cleanser becomes hard to squeeze out of a tube. As a result, we discovered that a weak acid skin cleanser which contains alkali salt of N-acylamino acid and a betaine-based ampholytic surfactant can beautifully solve the aforementioned problem, thus completing the present invention.
The object of the present invention is to develop a weak acid skin cleanser which solves the problem of the conventional technology, i.e. the hardness increases over time at room temperature or lower temperatures and therefore the skin cleanser becomes hard to squeeze out of a tube.
That is, the present invention provides a weak acid skin cleanser which characteristically contains alkali salt of N-acylamino acid, maltitolhydroxy aliphatic ether, water, and organic acid.
Also, the present invention provides a weak acid skin cleanser which characteristically contains alkali salt of N-acylamino acid, a hydroxy alkyl ether carboxylic acid-based anionic surfactant, water, and organic acid.
Furthermore, the present invention provides a weak acid skin cleanser which characteristically contains alkali salt of N-acylamino acid, polyethylene powder, water, and organic acid.
Also, the present invention provides the aforementioned weak acid skin cleanser wherein said alkali salt of N-acylamino acid is N-acylglycine salt.
Furthermore, the present invention provides the aforementioned weak acid skin cleanser wherein the content of said alkali salt of N-acylamino acid is 1-5.0 wt % of the total amount of the weak acid skin cleanser.
Also, the present invention provides the aforementioned weak acid skin cleanser wherein the content of said maltitolhydroxy aliphatic ether is 0.01-5 wt % of the total amount of the weak acid skin cleanser.
Furthermore, the present invention provides the aforementioned weak acid skin cleanser wherein the content of hydroxy alkyl ether carboxylic acid-based anionic surfactant is 0.1-20 wt % of the total amount of the weak acid skin cleanser.
Also, the present invention provides the aforementioned weak acid skin cleanser wherein the content of said polyethylene powder is 0.5-5 wt % of the total amount of the weak acid skin cleanser.
Furthermore, the present invention provides the aforementioned weak acid skin cleanser additionally containing a water soluble compound with a hydroxyl group.
That is, the present invention provides a weak acid skin cleanser which characteristically contains alkali salt of N-acylamino acid, a betaine-based ampholytic surfactant, water, and organic acid.
Also, the present invention provides the aforementioned weak acid skin cleanser wherein said alkali salt of N-acylamino acid is N-acylglycine salt.
Furthermore, the present invention provides the aforementioned weak acid skin cleanser wherein said betaine-based ampholytic surfactant is one or more compounds represented by the following chemical formulas (1), (2), (3), or (4). 
(In this formula, R1 denotes an alkyl group or alkenyl group with a carbon number of 8-21, R2 and R3 denotes alkyl groups with a carbon number of 1-3, and n denotes an integer 1-4.)
Also, the present invention provides the aforementioned weak acid skin cleanser which is in a paste form wherein the content of the alkali salt of N-acylamino acid is 5-50 wt % and the content of the betaine-based ampholytic surfactant is 0.1-30 wt % of the total amount of the weak acid skin cleanser.